1. Field of the Invention
The present invention relates to optical lenses for glasses and contacts, more particularly, to an improved lens with Rugate filter specifically designed as protection against macular degeneration (prescription and non-prescription glasses and sunglasses) by reducing harmful light transmission and ocular photochemical damage.
2. Description of the Background
The goal of most protective eyewear (including high-end sunglasses) is to provide a particular light transmission profile that yields the highest protection and perfect vision under all light conditions. To accomplish this goal the lenses for protective eyewear often incorporate numerous layers and coatings all of which combine to give a particular profile for a particular purpose. The ocular hazards from ultraviolet solar radiation are well established. Ultraviolet radiation falls within a range of wavelengths below visible light, generally between 100 and 400 nanometers. Long UVA radiation occurs at wavelengths between 315 and 400 nanometers. UVB radiation occurs between 280 and 315 nanometers. UVC radiation occurs between 200 and 280 nanometers. Wavelengths between 100 and 200 nanometers are known as vacuum UV. Vacuum UV and UVC are the most harmful to humans, but the earth's ozone layer tends to block these types of ultraviolet radiation. According to Prevent Blindness America, the American Academy of Ophthalmology, and the American Optometric Association, the hazards from ultraviolet exposure include eyelid cancer, cataract, pterygium, keratitis, and macular degeneration. Cataracts are a major cause of visual impairment and blindness worldwide. “We've found there is no safe dose of UV-B exposure when it comes to risk of cataract, which means people of all ages, races and both sexes should protect their eyes from sunlight year-round.” Infeld, Karen, Sunlight Poses Universal Cataract Risk, Johns Hopkins Study http://www.eurekalert.org/releases/jhu-sunposcat.html (1998). The damage is cumulative.
Indeed, age-related macular degeneration (AMD) is the leading cause of blind registration in the western world, and its prevalence is likely to rise as a consequence of increasing longevity. Beatty et al., The Role of Oxidative Stress in the Pathogenesis of Age-Related Macular Degeneration, Survey of Ophthalmology, volume 45, no. 2 (September-October 2000).
More recently, the Age-Related Eye Disease Study (AREDS) was published. This was a major clinical trial sponsored by the National Eye Institute, one of the Federal government's National Institutes of Health. The AREDS investigated the history and risk factors of age-related AMD, as well as how to reduce the risk of advanced age-related AMD and its associated vision loss. It was found that high levels of antioxidants and zinc significantly reduce the risk of advanced age-related AMD (reported in the October 2001 issue of Archives of Ophthalmology).
What is less well-known is that visible blue light can contribute to age-related AMD and its associated vision loss, causing significant damage over time. The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. A typical human eye will respond to wavelengths from 400 to 700 nm. This visible blue light falling within the 400-475 nm range can also cause damage over time. A ten-year Beaver Dam Eye Study was recently completed and is reviewed in the Arch Ophthalmology, vol. 122, p. 754-757 (May 2004). This study proves a direct correlation between the incidence of blue light and AMD but does not attribute the correlation to any particular blue light wavelengths. A number of other references suggest a correlation between the visible blue light contribution of sunlight and AMD. See, for example, West S. K. et al., Arch. Ophthaomol., 1989; 107: 875; Cruickshanks K J et al., Arch. Ophthaomol., 1993; 111: 514; Young R. W., Survey Ophthaomol., 1988; 32: 252; Mitchell P. Et al., Survey Ophthaomol., 1997; 104: 770.
The present inventor contends that there is a significant need for protective lenses that block visible blue light in the 400-475 nm range. As the entire population is potentially exposed to sunlight, the odds ratio of 13.6 and 2.19 for high exposure to visible blue light and AMD represent quite robust evidence in support of the sunlight/AMD hypothesis. Consequently, a lens that dramatically reduces visible blue light (preferably in combination with a high degree of UVA and UVB protection, and without sacrificing visual acuity) will preserve visual function.
This transmission profile is difficult to achieve with conventional lens technology. The Food and Drug Administration only recommends that sunglasses, prescription or non-prescription, block 99% of UVB and 95% of UVA, and most sunglasses on the market meet these criteria. The American National Standards Institute (ANSI) rates nonprescription eyewear for their potential to protect the human eye against solar radiation. However, many feel that the ANSI Z80.3 standard falls short. For example, the Z80.3 standard does not require specific quantification of the precise transmittance of ultraviolet radiation, nor blue light or infrared radiation, or reflected or scattered solar radiation that is not transmitted through the lens but still reaches the human eye. Some sunglasses for outdoor enthusiasts can achieve 99% of both UVA & B reduction, but afford no protection against visible blue light. This is because the existing lens technologies only afford control over glare, as well as the UVA & UVB transmission profile of lenses. These technologies include polarizers, color filters and mirror coatings.
In an effort to develop a more comprehensive method of rating nonprescription eyewear for its ability to protect the eye against solar damage, the FUBI System has been proposed. The system presents a numeric value, from 0 to 100, for each of the three known harmful portions of the solar spectrum: ultraviolet (UV), blue/violet (B), and infrared (IR). A fourth value was determined for the fashion (F) of the eyewear as it relates to protection of the eye against reflected or scattered radiation that is not transmitted through the eyewear. With FUBI, the numeric value of the system for UV, B, and IR is derived by taking the average transmittance of radiation through each tested lens and weighting it by multiplying that value by a relative toxicity factor (RTF) for each waveband of solar radiation tested. The RTF is derived by multiplying the approximate level of radiation reaching a specified anatomic part of the eye at sea level for each wavelength tested by the inverse of the value of its action spectrum (sensitivity) on that part of the eye. This weighted average transmitted percentage of radiation was then deducted from 100 to derive the FUBI value for the UV, B, and IR range. The numeric value for F was derived by measuring the scattered or reflected light from five known sources of luminance at a fixed distance around opacified lenses on each tested frame. The FUBI system has been successfully used to rate a wide variety of known commercial products of nonprescription eyewear, and the highest rating is currently enjoyed by BAYZ Sunwear of Havre de Grace, Md. for their sunglasses which incorporate the technology of parent continuation-in-part Application Ser. No. 10/000,062 filed Nov. 3, 2001.
It is common to provide polarized lenses in sunglasses to eliminate the horizontal transmission of reflected light through the lenses of the glasses to the eyes of the wearer. The polarizing layer blocks light at certain angles, while allowing light to transmit through select angles. This helps to negate annoying glare reflected off other surfaces such as water, snow, automobile windshields, etc. A polarized filter is produced by stretching a thin sheet of polyvinyl alcohol to align the molecular components in parallel rows. The material is passed through an iodine solution, and the iodine molecules likewise align themselves along the rows of polyvinyl alcohol. The sheet of polyvinyl is then applied to the lens with colored rows of iodine oriented vertically in order to eliminate horizontally reflected light. The sheet of polyvinyl may be applied to a lens in one of two ways: the lamination method or the cast-in mold method. To polarize a glass lens, the lamination method is used whereby the polyvinyl filter is sandwiched between two layers of glass. For plastic lenses, the cast-in mold method is used whereby the polyvinyl filter is placed within the lens mold. Relevant prior art patents might be seen in the Schwartz U.S. Pat. No. 3,838,913 and Archambault U.S. Pat. No. 2,813,459. A significant benefit of polarized lenses is the elimination of glare from reflective surfaces such as water.
Color filters can also provide excellent ultraviolet obstruction properties. For example, U.S. Pat. No. 4,952,046 (SunTiger) discloses an optical lens with an amber filter having selective transmissivity functions. This is the original “Blu-blocker” patent for amber lenses that substantially eliminates ultraviolet radiation shorter than 515 nm. The lens is substantially transparent to wavelengths greater than 636 nm which are most useful for high visual acuity in a bright sunlit environment. Similarly, U.S. Pat. No. 5,400,175 (SunTiger) discloses an amber filter having a cut-on at 550 nm. However, color-differentiation is highly distorted due to the deep orange tint as their deep yellow-orange tint weakens color differentiation. Indeed, many tinted sunglasses do not provide the capability to recognize traffic lights or other necessary color cues.
Various mirror coatings have been available to the sunglass industry for decades. These mirror coatings can be applied to the front and/or back surface of a lens to further reduce glare and provide protection against infrared rays. Metallic mirrors comprise a layer of metal deposited directly on a glass lens to create the equivalent of a one-way mirror. See, e.g., U.S. Pat. No. 4,070,097 to Gelber, Robert M (1978). However, like polarizers, metallic oxide coatings are not color-selective and cannot selectively block visible blue light in the 400-475 nm range.
Currently, there are no protective lenses that can also block visible blue light in the 400-475 nm range without otherwise degrading the visible light transmission spectra. Consequently, it would be advantageous to provide a lens that can block visible blue light in the 400-475 nm range to dramatically reduce visible blue light, and preferably in combination with a high degree of UVA and UVB protection to preserve visual function.
Rugate filters are a less well-known lens technology in the context of protective eyewear. A Rugate filter is an interference coating in which the refractive index varies continuously in the direction perpendicular to the film plane. The addition of a rugate filter to a lens can potentially block visible blue and UV light, while allowing other visible light to pass unimpeded. Rugate filters are wavelength specific filters that have existed for about a decade. Their simple periodic continuous structures offer a much wider set of spectral responses than discrete structures, and they typically exhibit a spectrum with high reflectivity bands. This allows the possibility of making high reflectivity mirrors with very narrow bandwidth. Moreover, they can be formed so as not to distort bandwidths outside the stop-bands. In contrast to tinted lenses, this provides the capability to recognize traffic lights and other necessary color cues. An overview of Rugate filter technology can be found at Johnson et al., “Introduction to Rugate Filter Technology” SPIE Vol. 2046, p. 88-108 (November 1993), inclusive of how a simple rugate filter is derived from Fourier analysis. Other examples can be found in U.S. Pat. No. 5,258,872 “Optical Filter” by W. E. Johnson, et al. and disclosed in U.S. Pat. No. 5,475,531 “Broadband Rugate Filter” by T. D. Rahminow, et al. However, the prior art does not teach or suggest how to incorporate a rugate filter in an optical lens to provide an outstanding spectroscopic profile that can block visible blue light in the 400-475 nm range to dramatically reduce visible blue light, alone or in combination with a polarizing filter, and/or multi-layer dielectric mirror, and/or tinted lens a high to additionally give a high degree of UVA and UVB protection.
The present inventor has found that a Rugate filter can achieve this, while still yielding an exceptional light transmission profile under all light conditions that maximizes the degree of protection as well as clarity of vision. The present Rugate filter technology can be incorporated in ophthalmic lenses, sunglasses, polarized sunglasses, intraocular lenses and contact lenses.